Here’s the short list of the possible benefits of barefoot running: (1) Fewer injuries, due to “natural running;” (2) faster speed, due to increased running economy, from zero weight on feet.
Here’s the same list for running shoes: (1) Fewer injuries, due to outsole protection, midsole cushioning, and motion-control widgets; (2) faster speed, due to increased running economy, from muscle-sparing “work” performed by cushioned midsoles.
We runners may have to wait a long time for a resolution of point #1. But a new study from a highly-regarded running biomechanics lab sheds considerable light on point #2. And the winner is ….
There is no winner. It’s a tie. Running barefoot and running with modest cushioning yield the same metabolic efficiency, i.e., running economy. That’s because shoe cushioning spares the leg muscles just enough to balance out the zero-weight saving from no shoes.
That’s the conclusion reached by Rodger Kram and colleagues (principal author: Kryztopher D. Tung) from the University of Colorado. Their paper, “A Test of the Metabolic Cost of Cushioning Hypothesis during Unshod and Shod Running,” has been published ahead of print in Medicine & Science in Sports & Exercise.
All 12 subjects in the experiment were experienced barefoot or minimalist runners who landed at midfoot. They ran three times (in only thin socks, for hygienic reasons) on a specially outfitted treadmill. Once, they ran on the normal treadmill; it’s a hard-surface mill, not a bouncy one like those often found in homes or fitness gyms.
On two other occasions, they ran on the same mill, but with Nike phylon midsole foam affixed to the treadmill surface, either 10 millimeters or 20 millimeters thick. In other words, the subjects always ran barefoot, but sometimes on a foam-topped treadmill that simulated the cushioning of shod running. Under all three conditions, subjects were monitored for oxygen consumption and “metabolic power,” a measure of running economy.
Result? The runners’ metabolic power improved an average of 1.63% on the 10-millimeter foam compared to no foam. On 20 millimeters of foam, their power dropped back to the no-foam level.
In a separate test, the researchers compared the barefoot, no-foam condition with running in a pair of Nike Free shoes on the no-foam treadmill. There was no difference in running economy. Conclusion: “It appears that the positive effects of shoe cushioning counteracted the negative effects of added mass.”
The authors believe their findings have relevance for those who race long distances on the track. Many modern tracks are constructed to be super-hard, which produces fast sprint times. Yet most track shoes, even for distance runners, have almost no cushioning, just an outsole plate and spikes. A better approach: “Our results suggest that distance running spikes with midfoot/forefoot cushioning (or the use of racing flats) could enhance performance.”
Even better: Race barefoot on a track that has been “tuned” (cushioned) especially for distance running, like the 10-millimeter treadmill.
Readers shouldn’t assume that 10 millimeters is the optimal thickness for a running shoe midsole. It just happened to produce the best average result compared to the other cushioned condition in the reported paper. The researchers believe that more study is necessary, with a greater range of midsole thicknesses and types.
In addition, your weight and speed, among other things, will influence what midsole works best for you. Among the 12 subjects tested in the new paper, 4 required the least metabolic power with no foam, 4 with 10 millimeters, and 4 with 20 millimeters. As is usually the case, individual differences can be large.
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